Chemical process



United States Patent 3,424,638 CHEMICAL PROCESS Nelson S. Marans, SilverSpring, Md., assignor to W. R.

Grace & Co., New York, N.Y., a corporation of Connecticut No Drawing.Filed Nov. 2, 1964, Ser. No. 408,342 US. Cl. 156-272 6 Claims Int. Cl.C09 3/14; B01j 1/10 The present invention relates to the bonding ofmaterials and more specifically to improved method for laminating a widevariety of similar and dissimilar materials.

Many adhesive compositions have been disclosed in the prior art.Adhesive systems have been developed for practically all types ofmaterials and range fromsimple one component composition to complicatedmulti-component mixtures. These systems include the use of irradiationpolymerizable monomeric materials which are placed between layers ofmaterial to be bonded and polymerized by irradition.

.Prior art irradiation adhesive systems possess the inherent drawback inthat extended doses of irradiation are required to achieve the requireddegree of polymerization and bond strength. To date, an adhesive systemwhich may be applied to a wide variety of materials and which rapidlydevelops a high degree of bond strength with low doses of radiation hasnot been developed.

It is therefore an object of the present invention to provide aradiation activated adhesive laminating system which provides bondshaving a great degree of strength with a minimum of irradiation.

It is another object to provide a method of practically instantaneouslybinding a wide variety of materials which are similar and dissimilar inchemical composition using a relatively inexpensive and simple bondingagent and technique.

These and still further objects of the present invention will becomereadily apparent to one skilled in the art from the following detaileddescription and specific examples.

Broadly, the present invention contemplates a bonding method whichcomprises placing a relatively thin layer of acrylic acid between two ormore layers to be bonded, and subsequently polymerizing the monomer bysubjecting it to high energy ionizing radiation.

More specifically, we have found that two layers of similar ordissimilar materials may be rapidly and securely bonded by placing aliquid layer of acrylic acid between the layers and irradiating thecomposite structure with suflicient high energy ionizing irradiation topolymerize the monomer. It is found that by using this technique strongadhesive bonds may be formed between a wide variety of materials almostinstantaneously. The bond achieves full strength upon polymerization lbyirradiation and requires no further curing or setting period to acquireadditional permanency.

As indicated above, acrylic acid which is used as the adhesive agentherein is irradiation polymerized in a minimum amount of time. As amatter of fact, I have found that in my process acrylic acid polymerizesalmost explosively in a radiation field to prepare the laminatedstructures contemplated herein. It is also contemplated that minoramounts of CH =C containing monomers such as ethyl acrylate,Z-ethylhexyl acrylate, and a number of other alkyl acrylates andmethacrylates may be combined with acrylic acid to enhance or modify thebonding characteristics thereof. Modifying amounts of these monomersranging from about 1 to by weight of the acrylic acid used may becombined with the acrylic acid.

Substrates which may be bonded by the technique contemplated hereinincluded a wide variety of materials which are chemically similar ordissimilar. For example, the present technique may be used on organicpolymer materials such as polyethylene, polypropylene, polyamides,polyesters, polytetrafluoroethylene, polyvinyl chloride, polyvinylidenechloride, polystyrene, nylon, and polymet-hyl methacrylate. Thesesynthetic organic materials may be bonded to each other or they may bebonded to metallic materials such as aluminum, tin, lead, gold andsilver, steel, stainless steel, iron, and so forth. Furthermore, thefilms may be advantageously bonded to cellulosic materials such as paperand wood using the present technique.

The bonding operation is carried out by simply applying a relativelythin layer (on the order of 5 to about microns thickness ofpolymerizable monomer between the layers of materials to be bonded). Thecomposite structure is then subjected to high energy ionizingirradiation such as high energy electrons having energy of from about 10kev. to about 10 mev. The beam energy must be sufiicient to penetrate tothe acrylic acid layer and through this layer. The irradiation isconducted advantageously at room temperature, however, temperaturesranging from about 0 to about 100 C. may be similarly employed.

The composite structure is subjected to fromabout 0.1 to about 5.0megarads of ionizing irradiation. It is found that a minimum dosage rateof 3 l0 rads per second is required to give the desired bonding effect.Therefore, the irradiation is preferably delivered in a single dose orin as few doses as possible. The optimum condition is to polymerize asmuch of the acrylic acid as possible in a single pass. This method givesan exotherm which results in the best bonding. Temperatures of over 200C. have been achieved in the acrylic acid layer immediately afterirradiation. This exotherm appears to contribute to the superior bondingin the system. The acrylic acid used herein as the bonding agentpolymerizes with almost explosive rapidity, and hence, an instantaneousbond is formed.

We consider that a minimum number of free radicals over a very shortperiod of time is required to give this highly exothermic polymerizationand bonding. Radical concentrations of 1 l0 to 1 10 radicals per gramachieved in times of '1 to seconds appear desirabl'e.

Having described the basic aspects of the present invention, thefollowing examples are given to illustrate specific embodiments thereof.

Example 1 Numerous samples tabulated in the table below were bondedtogether using acrylic acid as the bonding monomer. The technique usedwas to cut 3 x 3 inch squares of the various materials and place 9"drops of acrylic acid on the lower square. The second layer of materialis then placed on the lower film to form a continuous liquid layer ofacrylic acid between the 2 films. The composite samples were then placedon a styrofoam insert on aluminum tray 10 inches from the acceleratorwindow and given a dose of 2 megarads of irradiation in two passes witha Van de Graafi electron accelerator which produced 2.0 mev. electronsand microampere beam current. A pass rate of 0.32 inch per second and apass 3 4 time of 3 minutes were used. The dose per pass therefore 5 TypeD film irradiated mixture of low and was calculated at 1.0 megarad. Thefilm materials used in high density plyethylenes1 m1l thick. theexamples below are described as follows (each nurn- 6 Mylar-polyesterfilmpolyethylene tereber refers to the example tabulated below):phthalate8 mils.

TABLE I 7 T6231: film polytetrafluoroethylene 2 Examples: Description ofmaterial and thickness 8 Polyvinyl chlorideplasticized but unstabi- 1Grex0.96 density polyethylenel mil lized-S mils.

thick. 9 Saran-polyvinylidene chloride-1 mil. 2 Polypropylenefilmgrade-4 mil thick. Aluminum foil-1 milReynolds wrap. 3 LOW density P ythylene fi1m-1 mil thick. 10 11 Polystyrene-biaxially oriented-4 mil. 4Type L filrnirradiated low-density poly- 12 Nylon- 6,6-nyl0n75 mils.

ethylene film-+1 mil thick. 13 Polymethylmethacrylatemils.

TABLE II 1 E E E E E E E E E E P E E E E E G E E E E E F G-E E E E E F-GE E E E E F E 4- E E E E G E F-G E G-E E P P E E E E P F F-G E E E P F-G6 E G F-G G P G P E P-F E P P E E E E F G F-G G F-G E G G s E E E F-GF-G P F-G E P E G G-E 9 E E E E E E E E E E E 10 E E E G-E E P-F F-G P EE P P 11 E E E E E E E E E F-G E 12 P F F P P P G E P F-G G-E 13 E G-E EP F-G P G G-E E P E G-E NOTE.-E Excellent bonding with one of polymerfilms tailing; G Good, one of polymer films failed and traces ofdelamination; F=Fair, both film failure and delamination; P= Poor,delaminated easily.

' TABLE III Acrylic Trans- Water Radiation (MR) acid Comonomer (Percent)Lamination parency of Nature of bond sensitivity (percent) bond (days)*3.0 90 N -vinyl2-pyrrolldone 10 7 3.0 80 d0 20 7 3.0 60 40 7 3.0 40 60 73.0- 20 80 7 3.0- 90 10 7 3.0-- 80 20 7 3.0 60 40 7 3.0 40 60 7 3.0 2080 Opaque do. 7 3.0 90 10 Excellent. Excellent. Flexible. 3.0 80 20 d dd 30+ 3.0 60 7 3 0 40 30+ 3 20 30+ 3 10 7 3 80 20 30+ 3 60 40 30+ 3 4060 7 3.0 90 10 7 3.0 80 20 7 3.0 60 40 7 3.0 40 60 30+ 3.0 20 80 7 2.090 10 7 2.0 80 20 30+ 2.0 60 40 7 2.0 40 60 7 2.0 20 80 7 2.0 90 10 302.0 80 20 30 2.0 60 40 30+ 2.0 40 60 30+ 2.0 20 80 30+ 2.0 90 10 7 2.080 20 7 2.0 60 40 30 2.0 40 20 7 2.0 20 80 7 1.0 90 10 30 1.0 80 20 301.0 60 40 30+ 1.0 40 60 30+ 1.0 20 80 30+ 0.5 90 10 7 0 5 80 20 0 7 0 6040 Slig 7 0 40 60 Flexible. 30+ 0 20 80 d Gurnm 7 3 90 10 t Brittle. 7+3 80 20 d d 7+ 3 60 40 7+ 3.0 40 60 7+ 3.0 20 80 7+ 3.0 90 10 7 3.0 8020 7 3.0 60 40 7+ 3.0 40 60 7+ 3.0 20 80 7 3.0 90 10 7 3.0 80 20 7 3.060 40 7+ 3.0 40 60 7+ 3.0 20 80 7+ TABLE IIICntinued Trans- WaterComonomer (Percent) Lamination parency of Nature of bond sensitivitybond (days) 3. Fair. Good. Slightly brittle 7 3. do. .,do Brittle 7 3..do .do. .do. 7 do ..do do 7 3. d0 do do 7 3. 10 Excellent. 7+ 3. 20 7+3. 40 7 3. 60 7+ 3. 80 7+ 3. l0 7 3 20 7 3 40 7 3 60 7+ 3. 80 7+ Watersensitivity was tested by placing the sample in Water at 25 C. andmeasuring the time to delamination at 1, 7, 14 and 30 days.

Example II To illustrate that acrylic acid may be admixed with variousratios of copolymerizable monomers to obtain bonds having variousproperties the runs tabulated below were conducted. The radiation dosagewas varied from 0.5 to 3.0 MR using 2 mev. electrons. All doses weredelivered within a 10 second period. Sheet polyethylene was bonded tosheet polypropylene and four drops of acrylic acid comonomer mixture wasapplied per square inch of bonded area.

The above examples clearly indicate that a wide variety of similar anddissimilar materials may be readily and quickly bonded using thetechnique described herein.

I claim:

1. A method for bonding which comprises applying a layer of acrylic acidbetween layers of material to be bonded, and polymerizing said acrylicacid by irradiation with high energy ionizing irradiation whereupon saidlayers become spontaneously and securely bonded.

2. The method of claim 1 wherein from about 0.1 to about 5 megarads ofirradiation is applied.

3. The method of claim 1 wherein said radiation consists of electronshaving an energy in excess of that required to penetrate the thinner ofthe two materials to be bonded and the liquid acrylic acid layer.

4. The method of claim 1 wherein said layers of materials are selectedfrom the group consisting of poly- References Cited UNITED STATESPATENTS 3,157,560 11/1964 Livingston et a1. 204159.16

OTHER REFERENCES Horn: Acrylic Resins, Reinhold, New York, 1960, pp. 8and 25.

DOUGLAS J. DRUMMOND, Primary Examiner.

US. Cl. X.R.

1. A METHOD FOR BONDING WHICH COMPRISES APPLYING A LAYER OF ACRYLIC ACIDBETWEEN LAYERS OF MATERIAL TO BE BONDED, AND POLYMERIZING SAID ACRYLICACID BY IRRADIATION WITH HIGH ENERGY IONIZING IRRADIATION WHEREUPON SAIDLAYERS BECOME SPONTANEOUSLY AND SECURELY BONDED.